1. Field of the Invention
The present invention relates to a cleaning tape having a metal magnetic thin-film or a metal thin-film formed through vapor deposition.
2. Description of the Related Art
In the field of, for example, video tape recorders (VTRs), there are strong needs for improving recording density in order to obtain high quality images. The degradation of picture quality due to the accumulation of dirt on the surface across which the head slides becomes more prominent as the recording density becomes higher, the wavelength shorter and the tracks narrower. This makes cleaning tapes essential for general users to maintain the system in good conditions. High cleaning performance is required of cleaning tapes.
In digital magnetic recording systems, it is typical to employ magnetoresistive (MR) heads or giant magnetoresistive (GMR) heads in order to achieve higher recording density. It is believed that no electrostatic discharge damage takes place with inductive type heads which have been used conventionally. However, magnetoresistive heads such as MR heads (AMR (anisotropic magnetoresistive) heads), GMR heads, or tunnel magnetoresistive (TMR) heads are susceptible to electrostatic discharge damage.
GMR heads and TMR heads are even more susceptible to electrostatic discharge damage as compared to MR heads. Electrostatic discharge damage occurs at about 100 volts in MR heads, whereas electrostatic discharge damage in GMR heads occurs at about 30 volts and at about 30 to 50 volts in TMR heads. In order to protect MR heads and the like from electrostatic discharge damage due to static buildup in the cleaning tape itself, it is necessary that the electrical resistivity of the surface of the cleaning tape, which contacts the head, be 1×107 Ω/inch2 or below.
On the other hand, if the electrical resistivity of the cleaning tape is too low, leakage current from outside that reaches the head by way of the cleaning tape may lead to electrostatic discharge damage to MR heads and the like. In order to prevent such electrostatic discharge damage to MR heads and the like that occur with the cleaning tape as a conductor, it is necessary that the electrical resistivity of the cleaning tape be 1×103 Ω/inch2 or above.
It is preferable that the electrical resistivity of the tape be high in order to prevent electrostatic discharge damage due to a large current flowing momentarily into the head. As such, the electrical resistivity of a cleaning tape for GMR heads is set slightly higher than the electrical resistivity of a cleaning tape for MR heads. Specifically, the electrical resistivity of a cleaning tape for MR heads is set at about 1×103˜1×106 Ω/inch2, while the electrical resistivity of a cleaning tape for GMR heads is set at about 1×103˜1×107 Ω/inch2, preferably at about 1×106 Ω/inch2.
In magnetoresistive heads such as MR heads and GMR heads, the magnetic resistance varies with the depth of the effective surface of the head. Since the output of a magnetoresistive head depends on the magnetic resistance, as it wears and the magnetic resistance changes, the reproduced output waveform becomes larger as compared to before wearing. When the change in magnetic resistance exceeds a certain value, the adjustment of a head amplifier adjusted with an initial value is shifted, and the reproduced waveform becomes non-linear. It is therefore required that wearing be kept to a minimum in magnetoresistive heads.
Conventionally, as cleaning tapes for magnetic heads, coated type tapes, in which a non-magnetic substrate is coated with a magnetic coating including ferromagnetic particles and a binder, have been used. A coated type cleaning tape is disclosed in, for example, Japanese unexamined patent publication no. 2000-57541.
In such a coated type cleaning tape, a magnetic layer formed by applying a magnetic coating contains an electrically non-conductive binder and additives. It is therefore impossible to reduce the electrical resistivity below 1×107 Ω/inch2 or below. In order to reduce the electrical resistivity of cleaning tapes to 1×107 Ω/inch2 or below, it is necessary to form the magnetic layer through vapor deposition or other methods in which no binder or the like is mixed in the magnetic layer.
An evaporated cleaning tape in which a magnetic layer is formed by vapor deposition is disclosed in Japanese unexamined patent publication no. 1996-315327. This cleaning tape is characteristic in that when it is applied to a high definition digital VTR system, cleaning related information can be displayed visually while cleaning.
Although it is possible to visually display cleaning related information with coated type cleaning tapes if the system has a recording density that is lower than the recording density of high definition digital VTR systems, the electromagnetic conversion performance required for such visual display in high definition digital VTR systems cannot be obtained with coated type tapes. In line with the improvement in the recording density of magnetic recording medium in recent years, the tape width is decreased to, for example, 8 mm or less.
Currently, securing sufficient electromagnetic conversion performance with such narrow tapes is only possible with evaporated tapes. Even if the magnetic layer is formed by vapor deposition, desired cleaning effects and electromagnetic conversion performance cannot be achieved unless the surface characteristics of the magnetic layer are controlled appropriately.
Accordingly, in the cleaning tape disclosed in Japanese unexamined patent publication no. 1996-315327, surface protrusions are formed on the surface of a non-magnetic substrate with a predetermined density using two types of particles having different sizes. By varying the size and the density of the particles, the surface characteristics of the magnetic layer are adjusted.